1. Field of the Invention
The present invention relates to container forming machines, and in particular to a new method and apparatus for forming containers of a type having rigid sidewalls that are uniquely attached to a central fiberboard or plastic wrap.
2. Description of the Prior Art
A wide variety of paperboard shipping and storage containers are known in the art. An equally wide variety of container forming machines are also known in the art. Among the more common uses of such containers are for the packing, shipment and storage of fresh fruit and vegetables, and for the storage and shipment of pre-packaged goods (e.g. cans of soup, bottles of beverages, jars of jelly, bags of rice, cartons of cereal, etc.). Such containers are typically made from paperboard materials such as, without limitation, single face corrugated, single wall (double-faced) corrugated, double wall corrugated, triple wall corrugated, container board, boxboard, linerboard, fiberboard and cardboard. There are many well known container styles that have been developed over the years, each being optimally suited for one or more particular products or industries.
Shipping and storage of fresh fruits such as table grapes pose particular problems because of the delicate nature of fruit, the cold temperatures in which the fruit is stored, and the need to pack, ship and store large quantities of fruit in reasonably sized containers.
Many paperboard containers have reinforced sides or end panels in order to improve stacking strength, such as that disclosed in U.S. Pat. No. 4,905,834. However, even with such reinforcements, these containers still suffer from significant stacking strength limitations because they are made of paperboard. The paperboard could easily become wet from such sources as rain, condensation in cold storage, ruptured fresh fruit, or the like, thereby losing stacking strength. Adding wax to such paperboard may improve resiliency, but also renders the paperboard container unrecyclable.
One known shipping container provides one or more fiberboard panels between two wooden end plates, the panels being nailed to the end plates. While the use of wood improves stacking strength of the container, such containers tend to slide against each other, particularly in taller stacks. In addition, the wooden end plates in the container may damage the fruit, the wood is expensive, and disengaging the nails and fiberboard from the wood panels is cumbersome, making such containers difficult to reuse or recycle. Replacing the wooden side panels of such containers with injection molded polypropylene can reduce the cost, but does not resolve the sliding problem, and exacerbates the recycling problem.
In response to these problems, a new container has been developed which is the subject of U.S. Pat. No. 5,497,939. This new container uses two specially designed plastic sidewalls (end panels) and a panel for attachment between them. Each plastic sidewall has stacking tabs on the top, corresponding receiving slots on the bottom, and a set of locking slots on the bottom and side edges thereof. The attachable panel includes a series of protruding lockable tabs along its sides, each tab having at least one opening therein. The panel is positioned between the two sidewalls such that the edges of the panel wrap around the sidewalls, the tabs on the panel engaging with the locking slots on the sidewalls to form a sturdy, stackable container. Forming such a container without the use of adhesives or nails allows the panel wrap to be cleanly and easily disengaged from the sidewalls, thereby allowing the wrap to be recycled and the sidewalls to be reused. Accordingly, a method and apparatus are needed to form the unique containers of U.S. Pat. No. 5,497,939.
In particular, such containers require an apparatus which is capable of firmly holding the plastic sidewalls in place, attaching the panel wrap to the sidewalls by engaging the tabs on the wrap with the locking slots on the bottom and side edges of the sidewalls, and preventing the central portion of the panel wrap from being bent or deformed--all without using adhesives or nails.
Virtually all paperboard machines use adhesives to bond the various pieces of the paperboard container together. Some machines fold a single paperboard blank into a container having a particular shape, such as that shown in U.S. Pat. No. 3,858,489; and others fold and eventually join together two or more paperboard pieces to form the container, such as that shown in U.S. Pat. No. 4,238,188.
U.S. Pat. No. 4,637,544 discloses a container box having two synthetic side walls connected by a folded sheet of cardboard. However, both side walls include U-shaped grooves recessed in the faces thereof for receiving the edges of the folded cardboard piece. A set of teeth found in the grooves are used to fasten the side walls to the folded cardboard piece. Thus, the cardboard piece must first be folded and placed in an exact position, then each of the side walls must be precisely inserted over the ends of the folded piece in order for the edges of the piece to fit into the grooves and engage the teeth. This patent does not disclose any apparatus for accomplishing this task. By contrast, the panel of the container formed by the present invention interlocks with locking slots on the exterior edge surfaces of the sidewalls, by engaging a series of panel tabs with locking slots in the sidewalls.